The linear motion guide units have been extensively applied in recent years between relatively sliding parts for linear reciprocating mechanism used in increased industrial fields including machine tools, various assembling machines, conveyors, and so on. With the prior linear motion guide units of the sort of roller bearings, the lubricating members are installed in the end caps at the opposite ends of the slider in the traveling direction of the slider to apply lubricant around the rolling elements while rolling through the turnaround passages in the end caps, thereby realizing virtual maintenance-free operation for lubrication.
One of prior linear motion guide units lubricated with any lubricant-impregnated polymers is disclosed in Japanese Laid-Open Patent Application No. H10-78 032, in which an end cap has a curved passage of a looped circuit through which rolling elements circulate and an inside wall surface of the curved passage is built in part of a return guide constituted with a skeleton for reinforcement and a lubricant impregnated polymers. The return guide fits into a semi-circular recess cut in the backside of the end cap. The return guide constructed as stated just earlier, however, poses a challenge that it is tougher to contain or preserve enough amount of lubricant as the proportion of the skeleton for reinforcement gets higher relative to the lubricant impregnated polymers.
In Japanese Laid-Open Patent Application No. 2001-82 469, there is disclosed a linear motion guide unit in which a return passage in the slider is made of sintered resinous material of porous or open-cellular construction. A through-hole to define the return passage in the slider is constituted with a tubular member of porous compact impregnated with lubricant to apply the lubricant around the rolling elements while running through there. Nevertheless, this prior linear motion guide unit, as in need of making the through-hole inside the return passage large in diameter, isn't ready for the miniature or downsized linear motion guide units.
A linear motion guide unit in which application of lubricant around the rolling elements is done in the turnaround passage has been already known and disclosed, for example in Japanese Laid-Open Patent Application No. 2007-100, 951. With the prior linear motion guide unit, the turnaround passage in the end cap has the wall surface constituted in part with a porous compact impregnated with lubricant to expose an applicator surface of the porous compact to apply the lubricant around the rolling elements while rolling contact with the porous compact. However, such construction as stated earlier could be ready for only relatively large type of the linear motion guide unit.
In Japanese Laid-Open Patent Application No. 2008-82 433, there is disclosed the linear motion guide unit in which application of lubricant around the rolling elements is done at the turnaround passage to make the lubrication system simpler than ever in construction, along with maintenance-free for steady and positive oil lubrication. With the prior linear motion guide unit constructed as stated earlier, a porous compact impregnated with lubricant is placed in the end cap in such a way as to expose an applicator surface of the porous compact to the turnaround passage. Thus, the porous compact makes contact with the rolling elements running through the turnaround passage to supply the lubricant around the rolling elements.
A slider in the linear motion guide unit to ensure the smooth rolling and positive lubrication of the rolling elements is known and disclosed, for example in Japanese Laid-Open Patent Application No. 2009-63 059. With the prior slider as recited above, a porous compact impregnated with lubricant fits in the end cap to expose an applicator surface thereof to a curved surface of the turnaround passage to apply the lubricant around the rolling elements while coming into rolling contact with the applicator surface. The construction as recited earlier could be ready for especially rolling elements (rollers).
In Japanese Laid-Open Patent Application No. 2009-68 611, there is disclosed a slider which can ensure the smooth rolling and positive lubrication of the rolling elements even though produced at low costs without strict dimensional control. With the prior slider, porous compacts impregnated with lubricant are exposed to the turnaround passages in the end caps in such a fashion that their applicator surfaces intersect with the outside curved halves of a pair of the turnaround passages to come into touch with the rolling elements to thereby apply lubricant around the rolling elements. The construction as recited earlier could be ready for especially roller rolling elements.
Other linear motion guide unit in which balls are selected for the rolling elements is known and disclosed, for example in Japanese Laid-Open Patent Application No. 2006-38 195. With the prior linear motion guide unit, the cylindrical slider is composed of a carriage provided therein with a lubricant reservoir, and end caps fastened to the opposite ends of the carriage and provided therein with lubricant applicators. The rolling elements are lubricated inside the turnaround passages in the end caps.
Recently, the linear motion guide units recited earlier have been increasingly needed to be maintenance-free for lubrication over a long-lasting operation. Nevertheless, the linear motion guide units of miniature type, because of being much downsized in their contour dimensions, are really impracticable to realize maintenance-free for lubrication due to lack of space for the provision of a lubricating member. When an attempt was made to apply the conventional sleeve or tube of a lubricating member to the miniature linear motion guide units, the lubricating member inevitably would get too small in thickness to reserve therein sufficient lubricant enough to keep the linear motion guide units against any lubrication failure such as binding or seizure between parts. Contrary to the above, the lubricating member capable of reserving ample amount of lubricant is required making the lengthwise bore for the return passage larger in the carriage in the slider. This poses other challenges in that the carriage degrades in rigidity or stiffness because of the large bore and at the same time material around the large bore may become very lean in thickness.
Meanwhile, installation of the lubricating members in the end caps has been heretofore employed in the roller-type linear motion guide units. A new attempt has been done to apply the installation of the lubricating members in the end caps to the ball-type linear motion guide unit, especially the miniature linear motion guide unit using a guide rail of not more than 3 mm wide and ball rolling elements of not more than 1 mm in diameter. Further, the miniature linear motion guide unit with the lubricating members installed in the end caps has been proved successful in virtual maintenance-free operation for lubrication over a long-lasting period.